The primary objective of the proposed research is to gain information on the immunochemistry of human C5a anaphylatoxin. The first approach will be to improve the method of C5a generation and isolation which will permit higher yields and allow structural studies. Efforts will be directed toward the elucidation of the amino acid composition of C5a, identification of its COOH-terminal amino acid residue and the relation between its structure and biological activity. These studies will allow a comparison of the structure of human C3a and C5a and of the C5a from other species. As a second approach we will examine the capacity of C5a to release histamine from human skin and the ultrastructural lesions associated with this effect. Further, inhibitors effective in preventing non-anaphylatoxin histamine release will be used in vitro to determine their effect on the mechanism of histamine release by anaphylatoxins. We will also investigate the effect of chemical modifications of the C5a primary structure on the expression of its biological activity. Previous experiments employing the serum of patients in shock who have had in vivo activation of the complement system and thereby have been depleted of complement indicated that C3a is present and might be operative in analphylactic and/or endotoxic shock. Under these circumstances, for reasons yet to be elucidated, the anaphylatoxin inactivator levels in the serum were decreased. The availability of an immunochemical method for quantitation of the anaphylatoxin inactivator and of anaphylatoxins will permit new insight into the role of anaphylatoxins in the mediation of shock and of inflammatory responses. A search will also be made for genetic deficiencies of the anaphylatoxin inactivator.